1. Field of the Invention
The present invention relates to a thermal shield and hermetic seal that prevents deterioration of plastic insulation for electrical cable, such as communication cables, and to a method of extending the life of polyurethane chloride insulated cable (PIC) through reduction of exposure to heat, oxygen and ultraviolet radiation at access points along the PIC cable.
2. Background Information
Most communication cable used across the country since the mid-1950's has been polyurethane insulated cable, commonly called PIC cable, which has polymer insulation. This PIC cable includes copper conductors insulated in polyurethane enclosed in metallic and plastic sheaths. It is known that when the cable is kept undisturbed in it's original protective sheath or jacket, the cable underneath remains like new. However, problems occur in open-access splice closures and terminals where entry occurs on a somewhat regular basis for servicing. Exposure to heat and oxygen can slowly break down many polymer materials. High heat coupled with the presence of oxygen causes the breakup of the polymer chain as antioxidants escape. In addition, ultraviolet penetration, or photo-oxidation, accelerates cracking of the polymer insulation. Thus, once the opened cable is exposed to heat, oxygen, and ultraviolet radiation, the insulation around the conductors begins to deteriorate. After years of exposure, the insulation will begin to crack and flake off causing disturbance in a communication line using the cable. This disturbance is exacerbated by the presence of humidity or moisture. Cracked insulation conductors have zero oxidative induction time. Furthermore, patching the cracked insulation in a piecemeal fashion only remedies the problem in the short term. Thus, a goal has been to provide a remedy for the long term.
It is known in the building industry that using material with aluminum foil on roof sheathing lowers residential attic temperatures by approximately 30° F. It is also known to use sunshades having aluminum lining in parked vehicles to lower the inside temperature of the vehicle.
It is further known that wrapping aluminum foil around the splice bundle in black closures seems to reduce the temperature by 20° F. or more compared to those that do not have the aluminum foil. See Capadona and LaPointe, “An Examination Of Temperature Rise Inside Aerial Splice Closures”, Outside Plant, July 1988, pg. 22.
However, even with the reduction of temperature, exposure to oxygen remains a problem for the PIC cable. The present process is directed to the solution of the above-mentioned problems by providing a hermetic sealing process coupled with the use of an aluminum radiant shielding material that not only reduces the temperature, but also precludes the insulated wire from exposure to oxygen, thereby extending the life of the PIC cable.